1. Technical Field
This disclosure generally relates to heat pipes, and more specifically relates to a heat pipe that includes one or more reservoirs that provide demand-based charging.
2. Background Art
A heat pipe is used to transfer heat between a hot interface and a cold interface. The heat pipe includes a liquid in contact with a thermally conductive solid surface at the hot interface. When the hot interface heats up, the liquid turns into a vapor by absorbing heat from the hot interface. The vapor then travels along the heat pipe to the cold interface and condenses back into liquid, which releases the latent heat. The liquid then returns to the hot interface, and the cycle repeats. Heat pipes are highly effective thermal conductors, with an effective thermal conductivity orders of magnitude larger than for other heat transfer methods, such as a solid metal like copper.
Heat pipes are charged with a liquid. The amount of liquid in the heat pipe determines the performance of the heat pipe. As the rate of heat energy absorbed by the heat pipe increases, there is a possibility all of the liquid will turn to vapor. At this point, the temperature of the vapor within the pipe will begin to rapidly increase. As a result, the thermal resistance of the heat pipe increases exponentially. Consequently, most known heat pipes are usually overcharged or saturated with the liquid to avoid the increase of thermal resistance caused by turning all of the liquid into vapor. However, at lower heat energy rates, the performance of heat pipes that are overcharged or saturated is less than heat pipes that are charged with less liquid.
Heat pipes are commonly used in heat sinks for modern electronics, such as processors. To assure the heat sinks work properly when the processor is functioning at high power, the heat pipes in heat sinks are typically overcharged or saturated with liquid. This same heat pipe will work less efficiently at a lower power, meaning the temperature of the processor will be higher than if a heat pipe that were less charged with liquid were used. Thus, the designer of a heat sink that uses a heat pipe must make a tradeoff between performance of the heat sink at lower powers and performance of the heat sink at higher powers. Because excessively high temperatures can cause a catastrophic failure in a processor, the decision is usually made to overcharge or saturate the heat pipes in a processor heat sink so they can handle maximum processor power.